1. Field of the Invention
This invention relates generally to a method and apparatus for prechilling the warm tap water, fed into an ice maker machine to make ice cubes and the like, with the near freezing waste water ejected by the machine.
2. Description of the Prior Art
Ice making machines are now widely used, especially in warm climates, in hotels, schools, eating and drinking establishments, etc. Such machines use considerable electric or gas energy some of which is unnecessarily and needlessly wasted.
Ice makers are certified and rated in accordance with ARI Standard 810-91. Test conditions for standard ratings are 90.degree. F. ambient air, 70.degree. F. tap water, and about 30 psig water inlet pressure.
It is well known that productivity of an ice machine is a function, among other things, of its ambient air temperature and of the temperature of tap water used to make ice. The lower the tap water's temperature is, the higher will be the machine's ice yield during each ice "harvest". At the end of one or more harvest cycles, a considerable volume of unused 33.degree.-34.degree. F. cold waste water, in the vast majority of existing ice makers, is now being dumped down the drain, even though it has long been suggested to utilize the cold energy contained within the cold waste water ejected from the ice machine for prechilling its tap water requirements, as will now be described in more detail.
Even if the air temperature remains the same, lowering tap water's temperature by about 20.degree. F. can considerably increase the machine's ice yield. A temperature drop of 30.degree. F. in the summer has been a long-held desirata to owners of ice machines.
In addition to boosting the ice yield, other tangible benefits will be obtained including: savings on the amount of required floor space for the ice maker, on its cost and installation, and on its operating and maintenance expenses.
Usually the valuable space near an ice maker is very limited and crowded. Therefore, to obtain a higher ice production by replacing a smaller machine with a larger one may not be a desirable option.
But by using an effective, efficient and compact tap water prechiller, both the initial cost of a larger machine and its higher operating cost may be avoided; less heat will be injected into the room housing the ice machine thereby reducing the room's air conditioning load; less "wear and tear" will be experienced by the ice maker's active parts thereby prolonging their operational life; there will be less time for a mineral buildup on the machine's freeze plate and throughout its wetted areas; and the machine's bin will fill up faster with ice during peak demands because lowering the tap water's temperature will enable the ice maker to produce more ice in the same amount of time with little additional energy cost, or the same amount of ice in a shorter period of time.
Naturally, the above described cost savings and advantages prompted the expenditures of considerable efforts to arrive at practical water chilling methods and devices. Some of such prechillers had an insulated casing which enclosed a reservoir housing a heat exchanger fabricated from straight copper tubing or coiled. The casing has inlets for receiving the relatively warm tap water and the ejected cold waste water, an outlet to allow for discharging the prechilled tap water, and an overflow outlet to allow the excess waste water accumulated in the reservoir to escape.
The primary function of such a heat exchanger is to provide one path for the flow of the warm tap water, and another path for the flow of the cold waste water.
One type of heat exchanger had a copper pipe inside a plastic pipe. The potable water flowed in the copper pipe, and the cold waste water flowed through the annular space between the two pipes. This arrangement apparently was not successful perhaps due to the possible occlusion that may have occurred within the annular space due to mineral sediment accumulation.
U.S. Pat. No. 2,921,447 of Gottschalk describes a control device for discontinuing the operation of a water pump when other control devices might fail. In Col. 2, lns. 49-54 he suggests using a tap water prechiller as suggested in Howe's U.S. Pat. No. 2,775,100 which issued on Dec. 25, 1956.
Howe describes a common problem then faced by ice makers: "a substantial concentration of minerals of the type contained in the water used for the ice formation" (Col. 1, lns. 22-25) leads to an appreciable loss in the refrigeration capacity of the machine. Howe proposes discharging more of the cold water not used up during the ice formation (Col. 1, Ins. 32-35).
Howe very briefly also suggested to prechill the tap water. "As the water is discharged from the tank, it proceeds to a receiver 40 where it is passed in heat exchange relation with the water being supplied" by pipe 11 (Col. 4, lns. 26-29).
U.S. Pat. No. 4,338,794 of Hassis suggests prechilling the tap water as well as the refrigerant fluid in an ice cube making machine by using two copper coils within two chambers of an insulated casing. The potable water flows through one coil in one chamber, while in an adjacent chamber the other coil receives freon refrigerant. Cold waste water from the machine is allowed to flow through both chambers, resulting in a lowering of the temperatures of the tap water and of the freon.
In Frier's U.S. Pat. No. 2,403,272 is described a water cooler having an energy consuming refrigeration system, including a compressor and evaporator, which employs a vapor compression cycle during which the phase change of the freon is intended to achieve tap water cooling. The evaporator consists of a tank 1 housing a first coil 9 which surrounds a second coil 8 both made from very small diameter copper tubing. A hollow pipe 11, apparently made of metal, is mounted over inner coil 8. Pipe 11 has a bottom end open to the interior of tank 1 and a top end open to the cold water outlet 4. The tap water fills tank 1 and hollow member 11. As the freon flows under pressure spirally through coils 8, 9, it changes from liquid to vapor phase, while remaining at the same temperature throughout such change. The cold freon prechills both the water inside tank 1 and in pipe 11 as a result of its vaporization. The vaporized refrigerant leaves tank 1 and is returned back to the evaporator by the mechanical refrigeration system in liquid form to coils 8, 9 to start another cooling cycle as needed. Should a leak occur, the freon will contaminate the drinking water creating health and environmental hazards.
A water prechilling device is currently being sold under the trademark "Turbo-cool" by Adi/Turbo-Cool, 1901 Royal Lane Suite 100, Dallas, Tex. 75229. It apparently uses a heat exchanger, in the form of a straight copper pipe, within an insulated enclosed 4" cylindrical casing which collects the cold waste water from the ice maker. The casing has inlets for receiving the relatively warm tap water and the cold waste water, an outlet for discharging the prechilled tap water, and an overflow outlet to allow the excess waste water to escape. Apparently, the straight copper pipe receives the relatively warm tap water and discharges the prechilled tap water to the machine. In the heat exchange process, the waste water warms up due to the transfer of heat frown the warm tap water circulating through the straight copper pipe. The waste water's temperature rises while the temperature of the tap water flowing in the straight copper pipe decreases. This process is repeated after one or more ice harvest cycles, and the heat exchanger enters a new cycle of energy reclamation without using external energy, except that already contained in the cold waste water.
It is a general object of this invention to provide an effective, efficient and compact tap water prechiller, which can be adapted for use on a wide range of ice machines from small to large sizes, which achieves substantial savings on the machine's operating and maintenance expenses, and which reduces wear and tear on the machine's active parts. The novel prechiller reduces the mineral buildup inside its casing reservoir and substantially enhances the amount of heat that is being transferred in a unit of time across a unit of surface area of the heat exchanger's copper tubing, thereby optimally lowering the tap water's temperature per unit of casing volume, and correspondingly increasing the machine's ice productivity.